There seems to be a pretty straightforward top-to-bottom organization
There's just not. There's the current list of topics on the start page, but those can change at any time, they're not written to be read in any particular order, and there's no technical metadata identifying their relative positions that would even make this possible. There are also tons of other linked pages in the documentation, so that's not remotely the "entire documentation". (Just as one example, "Word Processor Integration" is a link to a landing page which links to other pages for each word processor, so that's not some single entry in an ordered list.)
We may try to show that main topics list in a sidebar at some point so they can be accessed more easily, but there still wouldn't be previous/next buttons on each individual page.
We may try to show that main topics list in a sidebar at some point so they can be accessed more easily, but there still wouldn't be previous/next buttons on each individual page.